Technical Field
The present disclosure generally relates to arrays of resistive change elements and generally relates to devices and methods for determining resistive states of resistive change elements in such arrays.
Discussion of Related Art
Any discussion of the related art throughout this specification should in no way be considered as an admission that such art is widely known or forms part of the common general knowledge in the field.
Resistive change devices and arrays, often referred to as resistance RAMs by those skilled in the art, are well known in the semiconductor industry. Such devices and arrays, for example, include, but are not limited to, phase change memory, solid electrolyte memory, metal oxide resistance memory, and carbon nanotube memory such as NRAM™.
Resistive change devices and arrays store information by adjusting a resistive change element, typically comprising some material that can be adjusted between a number of non-volatile resistive states in response to some applied stimuli, within each individual array cell between two or more resistive states. For example, each resistive state within a resistive change element cell can correspond to a data value which can be programmed and read back by supporting circuitry within the device or array.
For example, a resistive change element might be arranged to switch between two resistive states: a low resistive state (which might correspond to a logic 1) and a high resistive state (which might correspond to a logic 0). In this way, a resistive change element can be used to store one binary digit (bit) of data.
Or, as another example, a resistive change element might be arranged to switch between four resistive states, so as to store two bits of data. Or a resistive change element might be arranged to switch between eight resistive states, so as to store three bits of data. Or a resistive change element might be arranged to switch between 2n resistive states, so as to store n bits of data.
Within the current state of the art, there is an increasing need to scale and increase the cell density of resistive change element arrays. However, as technology is developed within the state of the art to provide increasingly smaller resistive change elements, the physical dimensions of individual array cells within a resistive change element array becomes, in certain applications, limited by the physical dimensions of in situ selection devices used within traditional resistive change element array cells. When data is read from an array of traditional resistive change element array cells an in situ selection device within each traditional resistive change element array cell is used to select the traditional resistive change element array cell that data is read from.